The present invention relates generally to the field of printer heads and more particularly to a mosaic needle printer head which uses printer needles actuated by the armatures of solenoid systems.
Some solenoid-operated mosaic needle printer heads utilize plunger armatures for actuating the printer needles during a printing operation. Thus the printing needles are rapidly reciprocated, being moved first in one direction upon excitation of the armature and then in an opposite direction by virtue of the biasing effect of a return spring.
In the manufacture of mosaic printer mechanisms, the attachment between the printer needles and the armatures of the individual electromagnetic systems presents a particularly vexing problem. One reason for this problem is the special fineness of the printer needles used in mosaic printers, the diameters of which are lessthan 0.4 mm. Another reason resides in the nature of the material of both the printer needle and the electromagnetic armatures. The material of which the printer needles are made must be extremely wear-resistant and breakage-resistant to produce a long useful like. Such materials, however, (as experience has shown) cannot be united with one another nor with other materials, such as, for example, those of electromagnetic armatures which must of necessity have good ferromagnetic properties, without great difficulty, and even then generally only to an incomplete extent. When plunger armatures are used in the solenoid systems for the actuation of the printer needles further difficulties in attachment between the printer needles and the armatures arise by virtue of the fact that in order to attach the printer needles to the plunger armatures, the latter must be provided with bores of correspondingly small diameters and adequate depth, formed centrally in the armatures. The manufacture of such bores to the requisite tolerances is an extremely expensive operation.
Welded and soldering connections are equally as expensive but in addition provide an additional problem in that damage to the structural materials may result as a consequence of the application of heat which is required in soldering and welding operations.
The connection problem is further compounded by the fact that in all circumstances it is necessary that the printer needle and the plunger armature are precisely axially aligned since otherwise the armature could cross-bind in the coil of the solenoid.
Unfortunately, the printer needles cannot be simply press-fit into the plunger armatures since, because of the small diameters involved, the materials do not have sufficient elasticity to produce a satisfactory frictional bond.
An object of the present invention is to provide a mosaic needle printer head which employs plunger armature solenoid systems and in which the connection between the printer needles and the plunger armatures are provided simply and inexpensively, while at the same time the connection is completely satisfactory and reliable.